Breast cancer. Coloured scanning electron micrograph (SEM) of a freeze-fractured section of a ductal carcinoma of a female breast. A mammary duct (red) has cancerous cells (pink) lining its walls. These malignant cells have their origin in the epithelial lining of the ducts. The ducts are the structures that channel milk to the nipple. Breast cancer is the most common cancer in women. The large majority of breast cancers are invasive ductal carcinomas such as this. Surgical removal is often combined with use of radiotherapy and chemotherapy. Magnification: x750 at 6x7cm size.